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66
Single-ended I/O pin assignments for LC models are shown in Table 14. The LC model does not require an I/O
cable. It is designed to connect directly to a backpanel connector.
9.7.1.3
Cables for low voltage differential drivers/receivers
The SPI-3 specification for differential impedance for LVD cables is 122.5 ± 12.5 ohms.
The maximum SCSI bus length between the terminators for a SCSI LVD point-to-point system (one initiator
and one target) is 25 meters (82 feet).
The maximum SCSI bus length between the terminators for a SCSI LVD multidrop system (up to 16 total SCSI
devices) is 12 meters (39.37 feet). However, implementation of this 12-meter total length is dependent on the
configuration of the system and the choice of cable. See Tables 17 and 18 for examples of recommended SCSI
LVD cable types and lengths.
It should be noted from the data in Tables 17 and 18 that shielded round twisted-pair cables can be used to
implement a 12-meter system, while twist-n-flat cables cannot be used to implement a 12-meter system due to
higher levels of attenuation and crosstalk. In addition, twist-n-flat cables with shorter sections of twist allow
greater crosstalk and their lengths must be reduced as shown in Table 18.
Table 17:
Example shielded round twisted-pair cables—into a multi-drive backplane
Differential
Cable
impedance,
description
nominal
30 AWG
130 ohms
solid
28 AWG
123 ohms
stranded
28 AWG
132 ohms
stranded
Table 18:
Example twist-n-flat cables—into a multi-drive backplane
Cable description
TPE, 22.25" twist, 1.75"
flat, (24" flat to flat), 30
AWG solid tinned copper
TPE, 8.1" twist, 1.75" flat,
(9.85" flat to flat), 30 AWG
solid tinned copper
TPE, 4.25" twist, 1.75"
flat, (6" flat to flat), 30
AWG solid tinned copper
9.8
Terminator requirements
Caution: These drives do not have onboard internal terminators. The user, systems integrator or host equip-
ment manufacturer must provide a terminator arrangement external to the drive when termination is
required. For LW/LWV drives, use terminator modules that plug between the SCSI I/O cable and
the drive I/O connector or on the end of a short I/O cable stub extending past the last cable connec-
tor. LC/LCV drives are designed to be plugged into a backpanel connector without cabling.
Single-ended
Single-ended
impedance,
capacitance,
nominal
maximum
90 ohms
17 pF/ft
80 ohms
19 pF/ft
85 ohms
20 pF/ft
Differential
Single-ended
impedance,
impedance,
nominal
nominal
131 ohms
93 ohms
131 ohms
93 ohms
131 ohms
93 ohms
Cheetah 73LP Product Manual, Rev. E
Time
Conductor DC
delay,
resistance,
nominal
nominal
1.36 ns/ft
0.113 ohms/ft
1.54 ns/ft
0.067 ohms/ft
1.50 ns/ft
0.065 ohms/ft
Single-ended
Time
capacitance,
delay,
maximum
nominal
15.3 pF/ft
1.45 ns/ft 0.105 ohms/ft
15.3 pF/ft
1.45 ns/ft 0.105 ohms/ft
15.3 pF/ft
1.45 ns/ft 0.105 ohms/ft
Maximum shielded round
twisted-pair cable length
for U160/U320
12 meters minus the SCSI
trace length of the backplane
12 meters minus the SCSI
trace length of the backplane
12 meters minus the SCSI
trace length of the backplane
Maximum
twist-n-flat
Conductor DC
cable length
resistance,
for U160
nominal
transfer rate
6.1 meters
(20.0 feet)
4.9 meters
(16.66 feet)
3.04 meters
(10.0 feet)
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